Objectives: Infant crying is particularly frustrating to caregivers in the first few months of life and the most common trigger for shaking and abuse. The effectiveness of the "Period of PURPLE Crying" prevention materials (DVD and booklet) designed to increase knowledge and change behaviors related to crying and the dangers of shaking was reported in North America. The aim of this study was to replicate the effectiveness of the "PURPLE" materials with mothers of newborns in Japan. Methods: In a randomized controlled trial, 201 parents received either "PURPLE" materials or analogous control materials on infant safety via mail within 2 weeks of birth. At 6 weeks, mothers completed a 4-day behavioral diary. At 2 months, participants completed a predefined 20-min structured telephone survey by an independent firm to assess knowledge and behavior. Results: Scores on crying knowledge scales (out of 100) were significantly higher in the intervention than control groups (56.1 vs. 53.1; difference = 3.0, 95% confidence interval [CI]: 1.0-4.9, p less than 0.005). Percentage of sharing of advice to walk away if frustrated by crying was significantly higher in the intervention than control groups (22.4% vs. 4.1%; difference = 18%, 95% CI: 7.4-29.1). Walking away during unsoothable crying was significantly higher in the intervention group than controls (0.085 vs. 0.017 events per day, rate ratio = 4.8, 95% CI: 1.1-21.2) by diary. Self-talk behavior scale (out of 100) tended to significance in the intervention group (16.6 vs. 8.9, difference = 7.7, 95% CI: -1.0 to 16.4, p less than 0.1). Conclusions: Crying knowledge, sharing of walk away information with others and walk away behavior when crying was unsoothable were higher for those who received intervention than control materials. The "Period of PURPLE Crying" materials may be useful in Japan as well as in North America for informing caregivers about the properties of infant crying and changing some behaviors related to infant crying and shaking. (UMIN Clinical Trials Registry register no. UMIN000001711.) (Contains 5 tables and 1 figure.)